Ask Your Question

I'm trying to substitute a value in a Laplace transform

asked 2018-11-26 23:09:05 -0500

bemol gravatar image

Hello, I'm trying to solve a DE by using Laplace transforms, but when I get the lapalce transfrom of my DE I get this part s*D0(0) and I don't know how can I substitute D[0], I tried D0(0) == -1) but I get an error that says that D is not defined, I can subs y(0) == 1 with no issues. So my question is how can I substitute the value for y'(0)=-1 in the Laplace transform.

thank you for your help !.

t = var('t')
s = var('s')
y = function('y')(t)

ED = diff(y,t,2)-2*diff(y,t)-3*y==4

ED_Lap = ED.laplace(t,s)
ED_Lap = solve(ED.laplace(t,s),laplace(y(t), t, s))
show(ED_Lap[0].rhs().subs(y(0)==1,D[0](y)(0)==-1).inverse_laplace(s,t)) # I don't know how to subs D
edit retag flag offensive close merge delete

1 answer

Sort by » oldest newest most voted

answered 2018-11-27 12:30:25 -0500

slelievre gravatar image

In fact, D[0](y) is one way to represent diff(y, t).

So just do:

sage: ED_Lap[0].rhs().subs(y(0)==1,diff(y, t)(0)==-1).inverse_laplace(s,t)
1/3*e^(3*t) + 2*e^(-t) - 4/3
edit flag offensive delete link more


Thank you very much for your time. Now it works !! :D

bemol gravatar imagebemol ( 2018-11-27 13:39:45 -0500 )edit

Glad this helped. Please formally accept the answer by clicking the "accept" button (the one with a tick sign). This way the question will be marked as solved in the list of questions.

slelievre gravatar imageslelievre ( 2018-11-28 00:39:21 -0500 )edit

Your Answer


Add Answer

Question Tools


Asked: 2018-11-26 23:09:05 -0500

Seen: 74 times

Last updated: Nov 27 '18